Prairie gull

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Prairie gull
Prairie gull in breeding plumage, here a random visitor in Australia

Prairie gull in breeding plumage, here a stray visitor in Australia

Systematics
Class : Birds (aves)
Order : Plover-like (Charadriiformes)
Family : Laridae
Subfamily : Seagulls (larinae)
Genre : Leucophaeus
Type : Prairie gull
Scientific name
Leucophaeus pipixcan
( Wagler , 1831)
Prairie gull in winter plumage
Flying prairie gull
A prairie gull in winter quarters in Peru

The prairie gull ( Leucophaeus pipixcan , syn .: Larus pipixcan ) or Franklin's gull is a medium-sized, black-headed gull that breeds primarily in the Prairie Pothole region in the northern Great Plains of North America and winters along the South American Pacific coast .

description

The prairie gull is with a body length of 32-38 cm slightly smaller than a black-headed gull ; the wingspan is between 85 and 92 cm, the weight 250-325 g. It is similar to the closely related Aztec gull , but is smaller and stockier with a relatively round head, blunter wings and shorter legs. It moves very quickly when foraging for food and is similar to smaller species of limescale such as plovers or sandpipers . Due to the unique moulting cycle with two annual full moults, the plumage hardly appears worn all year round.

Adult birds

Adult birds in breeding plumage wear a black head cap that extends to the upper neck and throat. Very wide, white eyelids contrast with this. The iris is blackish. The beak shows a dark red color with a dark band in front of the red or orange tip. During the breeding season, the beak darkens. The throat is scarlet. The plumage on the upper side is dark gray; The neck, underside and tail are white. In contrast to most other seagull species, light gray spring centers can be found mainly on the central control feathers, but this is sometimes only indistinctly visible in the field. Often the underside shows a pink tint. The upper wing is gray with a wide, white rear edge. The outer hand wings are white on the distal half with a subterminal black band, so that the black part of the wing tip appears lined with white inside and outside. In the sitting bird, the black and white pattern of the hand wings is clearly noticeable and differs significantly from the almost black hand wings of the Aztec gull. Legs and feet are red-orange to blackish brown and darken during the breeding season.

In winter clothes, the dark cap is reduced to the back of the head and a dark area in front of the eye and is also very streaky. The white eyelids are still noticeable. The beak is dark with a light tip, the feet very dark red or blackish.

Youth dresses

Juvenile prairie gulls have a streaky brown head cap that leaves out the area in front of the eye and extends to the back of the head. The white eyelids already stand out in the youth dress, but are still quite narrow. The neck is tinted gray-brown except for the sides of the chest. The underside is white, the upper side brown with whitish to light cinnamon-brown hems, which make the back, coat and shoulder feathers appear coarsely scaled. The arm cover field shows brown feathers with light hems. The large arm covers are monochrome brown-gray. Arm feathers and umbrella feathers are gray-brown with dark feather centers and broad white tips. The hand wing is blackish on the outside and becomes lighter gray on the inner hand wings, where the black part is reduced to a subterminal band. The white tips of the hand wings are very fine on the outer ones and become much broader towards the inside. The very light gray tail wears a narrow subterminal band, the outside of the tail is white. The bill, legs and feet are blackish.

In birds in the first winter, the half-present head cap is more black-brown; the white eyelids widen. The neck and sides of the chest still show traces of gray. Mantle and shoulder feathers are already dark gray, but some of them still have brown streaks. The white underside sometimes shows a pink tint on the belly. The upper wing resembles the youth plumage, but appears lighter due to the removal of the plumage. The bright hems of the umbrella feathers are sometimes almost completely worn away. The black tail band is still present. Some of the legs already show a reddish color.

In the first summer dress, the bird resembles adult animals except for the half-present head cap. The head cap looks more black than in birds in the first winter, the plumage is fresh due to the previous full moults. In the second winter, the only difference between the birds and adults is the large proportion of black in the hand wing. The white edge that lines the black of the wing tip inward is very weak, the white tips of the hand wings are only narrow. In the second summer, the birds are often almost completely colored. However, the cap may still be interspersed with white spots in the area of ​​the forehead, reins and chin.

voice

The vocal utterances of the prairie gull sound nasal and laughing. They are taller and less penetrating than those of the Aztec gull. The sound repertoire is very extensive. The main call is a squeaky pwäii . The shouts ( long call ) differs from that of most gulls. It starts with a kah , continues in a series of calls made of long pwäii calls that become faster and faster , which is often followed by a series of short sounds, and ends with a call in which the head is thrown back. A soft, deep and gurgling krruk can be heard as a voice- touch call - especially in foraging troops.

distribution

The breeding area of ​​the monotypical prairie gull is in the northern part of the North American prairie zone . It extends in the area of ​​the Prairie Pothole region from eastern Alberta through central Saskatchewan and southwestern Manitoba south to Montana , North and South Dakota and Minnesota . There are also scattered occurrences westward to central Oregon , southward to Utah and eastward to about northwestern Iowa . Individual breeding records are also available from other states, for example from Colorado , Kansas and California . An occurrence in British Columbia could not be confirmed. There are breeding season observations from Alaska .

hikes

The prairie gull is a long-distance migrant that overwinters mainly south of the equator along the South American Pacific coast. In addition to the swallow gull , it is the species of gull with the longest migration routes. The main wintering areas are between central Peru and central Chile . Smaller stocks remain in California, on the Gulf of Mexico , in Central America or on the Galapagos Islands . Some birds also migrate further south to the Strait of Magellan .

The colonies are evacuated in the second half of July, followed by dismigrations in all directions, which are limited to the area of ​​the prairie zone. The autumn migration begins in September and early October when larger swarms form and move south. The spring migration takes place between the beginning of March and the end of May, most birds return to the breeding areas in late April and early May.

habitat

The prairie gull breeds on shallow lakes with silting vegetation and in eutrophic , up to 1 m high flooded swamps, which are located on the North American prairie. It is less common in flooded meadows or on shallow reservoirs. The optimal habitat offers a not too dense vegetation of bulrushes , ledges or reeds , which is interspersed with open water bodies of variable sizes.

On the migration route, the species can be found in a wide range of wetlands. These include inland and coastal waters, floodplains or estuary landscapes. In winter quarters, the species mainly lives in the littoral , but can also be found up to 50 km inland. In the Andes it appears in lakes up to 2500 m high and socialises with the Andean gull , but usually it stays on the coast and can be found there together with gray gulls and Simeon gulls .

nutrition

The prairie gull's diet consists of insects and their larvae as well as earthworms . Occasionally there are also seeds and other parts of plants, small mammals , fish and fish waste, crustaceans , snails and other invertebrates . Food is often consumed in schools. In the breeding areas, insects are often captured in flight hunts over swamps or earthworms in the surrounding agricultural landscape when the seagulls follow plowing agricultural machinery. Fish and marine arthropods play a role in the wintering quarters .

During investigations at the Agassiz National Wildlife Refuge in Minnesota, the gulls looked for seeds, worms or insects on snow-free arable land after they arrived from their winter quarters. In late April, after the ice melted in the swamps, the hunt for flying insects increased; At times the whole colony was on a flight hunt over the reed and water areas. Between the beginning of May and the beginning of July the birds mostly followed the tractors as they plowed; In some cases, there were also mass occurrences of mosquitoes in the swamps.

Reproduction

The prairie gull breeds in colonies, the size of which can usually be a few hundred, sometimes well over 10,000 breeding pairs. The broods are very synchronous, so that the eggs are laid and hatched within a period of 21 days.

The arrival at the breeding sites is between the end of April and mid-May, the pairing usually takes place shortly before. The species is monogamous , but nothing is known about the length of a marriage. Territories are occupied within a short time after arrival.

The location of a colony in a body of water can change from year to year. It depends on the water level, density and distribution pattern of the vegetation. Places that are close to open water but still offer enough space for nest building and courtship are preferred as nest locations.

The nests are always built on the water. They stand on self-built platforms, on muskrat castles or on layers of floating parts of plants. They consist of a relatively flat platform, a ramp that leads into the water and a bowl that slowly grows during the breeding season, because as the nest slowly sinks into the water, it is constantly expanded. Before eggs were laid, nests in the Agassiz National Wildlife Refuge measured an average of 43 cm in diameter, at the beginning of the breeding season around 80 cm. About 14 cm protruded from the water, 11 were below the surface. Shortly before hatching, the nests had an average diameter of 102 cm, 20–40 cm were above and just as much below the water surface. Elsewhere, however, smaller nests have also been described. The nesting material is brought in from the surrounding area, and material is often stolen from other breeding pairs. Unguarded nests are completely removed within 2-3 hours.

Both sexes participate in nest building. If a male has not found a partner after more than a week, it can start building a nest platform on its own, but does not finish the nest until a female has been found.

The eggs are laid about a week after the nest has started to be built. The clutch consists of 2–4, but mostly 3 and only very rarely 4 eggs. These are smooth, oval to round-oval and speckled blackish on a cream-colored, yellowish, greenish or medium to dark brown background. The dimensions are approximately 52 x 37 mm. The eggs are incubated day and night, alternately by both partners. The incubation period is between 23 and 26 days.

The young are fed by both parents for about 35 days. The families stay together 8-10 days after the boys fledged. After about two weeks, the birds leave the colony.

Inventory development

The total population of the prairie gull is estimated at 470,000–1,500,000 adult birds. Mean values ​​from the years before 1994 indicate a population of at least 278,000 breeding pairs. The best survey data come from 1994 and 1995, when around 400,000 breeding pairs were identified, which may indicate a slight increase in the population. In the USA 100,000 breeding pairs were determined between 2005 and 2007, in Canada there were around 500,000 breeding pairs in 36 colonies in 2007. Five of them had more than 50,000 breeding pairs, the largest being on Whitewater Lake in Manitoba, where 92,000 breeding pairs were breeding.

Sources from the first half of the 19th century describe the prairie gull as a frequent breeding bird. In the late 19th century, however, the species appeared to be rare. Between 1915 and 1925 it became more common again. In the 1930s, at the time of the “ Dust Bowl ”, the species was threatened by habitat destruction due to large drainage projects.

There is some disagreement about the current inventory trend. Some authors assume a population decline of up to 90% in the 1990s. However, this is partly only based on the extrapolation of local observations, while increases were recorded elsewhere or there is no data at all.

Since the species often gives up complete colonies from one year to the next due to changing water levels, significant relocations take place and the birds often breed in remote swamp areas, the breeding populations are difficult to determine. Hardly any useful data can be obtained from Breeding Bird Surveys , the large-scale, state-organized breeding bird survey programs . Observations of the breeding season in the context of these investigations could often indicate more likely roaming birds without breeding success than actual breeding occurrences.

Nevertheless, a decline in several countries - mainly due to weather conditions and poor breeding success - is not unlikely since 1995.

In addition to weather conditions and changing water levels, the main causes of danger for the prairie gull are disturbances due to human activities at the breeding site. At the beginning of the breeding season they can lead to the abandonment of entire colonies. The El Niño weather phenomenon can lead to food shortages in the wintering quarters .

Systematics

The first specimen of this type was collected by John Richardson on the first Franklin expedition in 1823, probably on the Saskatchewan River . The bird was described by Joseph Sabine and found to be remarkable, but incorrectly assigned to Larus atricilla . After the second Franklin expedition in 1830, Richardson named the species Larus franklinii , which name lasted for over a century. However, Richardson did not publish the description until 1832, so Johann Georg Wagler's first description of a bird collected in Mexico from 1831 as Larus pipixcan has priority .

After a reorganization of the gulls (Laridae) based on genetic findings after 2005, the species is now placed in the genus Leucophaeus together with four other New World species .

literature

Individual evidence

  1. ↑ a b c d Olsen / Larsson (2003), p. 511, see literature
  2. ↑ a b Burger / Gochfeld (2009), section Appearance , see literature
  3. ↑ a b c Olsen / Larsson (2003), pp. 511f, see literature
  4. ↑ a b Glutz v. Blotzheim, p. 266, see literature
  5. ↑ Präriemöve, Jauchzen (long call) audio sample
  6. ↑ Burger / Gochfeld (2009), section sounds , see Literature
  7. ↑ Burger / Gochfeld (2009), section Distribution , see literature
  8. ↑ a b Burger / Gochfeld (2009), section Migration , see literature
  9. ↑ Glutz v. Blotzheim, p. 267f, see literature
  10. ↑ a b Glutz v. Blotzheim, p. 268, see literature
  11. ↑ a b c Burger / Gochfeld (2009), Habitat section , see literature
  12. ↑ a b Burger / Gochfeld (2009), section Food Habits , see literature
  13. ↑ a b c d e f g Burger / Gochfeld (2009), section Breeding , see literature
  14. ↑ a b c d e f g Burger / Gochfeld (2009), section Demography and Populations , see literature
  15. ↑ BirdLife Species Factsheet, see web links
  16. ↑ a b Burger / Gochfeld (2009), introduction, see literature
  17. ↑ J.-M. Pons, A. Hassanin, P.-A. Crochet: Phylogenetic relationships within the Laridae (Charadriiformes: Aves) inferred from mitochondrial markers . Molecular Phylogenetics and Evolution, Volume 37, Issue 3, December 2005, pages 686-699 doi : 10.1016 / j.ympev.2005.05.011

Web links

Commons : Prairie Gull ( Leucophaeus pipixcan )  - Collection of images, videos and audio files